[bluGill]

Heat pumps work down to -25C. Cold climates get colder than that. Sure most cold climates are typically above that, but it only takes one night every 10 years to hit those temperatures and a heat pump alone does not work. You need a backup. Of cousre once we have a backup we can ask if it is cost effect - heat pumps get less efficient as temperatures go down - when you need the most heat, so it may be most cost effective to install a heat pump that doesn't even work to that cold (perhaps it does but is under sized?) and just use backup heat when it is cold.

[wtallis]

One night where the outside temperature gets below -25C is not a serious problem. If you had the heat pump keeping your house at a comfortable temperature the day before, you aren't going to die of hypothermia or have pipes freeze overnight. You'll just wake up to a house that's chilly inside and takes most of the day to get back up to where you want it.

Sustained cold spells are where you need an alternative heat source.

[google234123]

Also electric heaters are dirt cheap - get a bunch 20$ ones

[wlonkly]

Or conveniently mount one inside your air handler!

[darkr]

I presume you’re talking about air source heat pumps here. Some will go down that far, but it’s not common. If installed in a location where winters will routinely see temperatures below -10/15 degrees C, it’s going to be far more efficient to do a ground source heat pump, ideally with a deep bore hole where you can get a heat source that is continually 10-20 degrees C

[doctorhandshake]

What you’re talking about is factored in to system design - it’s called the 1% design temperature.

https://www.greenbuildingadvisor.com/article/design-temperat...

As CP says, you design your system for the conditions 99% of the time, because designing for that last 1% leads to a terrible cost benefit calculation. Same reason you don’t daily drive an armored personnel carrier with a 300-gallon gas tank.

[micromacrofoot]

I live in one of these areas and I just use a couple electric space heaters a few days a year - my mini splits are still great otherwise.